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Op Amp Contest: Go Down An Octave, No FFT, No PLL, No Oscillator! [Hackaday]
We like a project that makes us think, and that was certainly the case with [MS-BOSS]’s octave downshifter that’s an entry in our current op-amp contest. Instead of resorting to an FFT, or a PLL, it uses a technique best described as a custom analogue computer to implement the maths of octave downshifting. It’s an extremely clever approach, and we don’t mind admitting took us more than one read to understand how it works.
Just as you would with any mathematical problem, he’s split the job of halving the frequency into its constituent mathematical functions. The square root calculation circuit is probably the one that most required the dredging up of dimly-remembered analogue circuitry undergraduate courses for us.
The result is a fascinating read that’s well worth taking the time to understand if you have any interest in analogue electronics. It’s by no means the easiest way to make this particular effect in 2023, as we’re much more used to seeing our community make digital effects, but if you fancy yourself as any kind of op-amp designer, you really need to give it a look.
